Vain efforts?

The task of reviving extinct animals may be impossible

Marina Astvatsaturyan, "Search"

An extinct species of rats that once lived on Christmas Island in the Indian Ocean may put an end to scientists' hopes for the revival of more famous extinct animals. Currently, no species has been revived yet.

In order to revive an extinct animal, you first need to sequence its genome, and then edit the DNA of the most closely related animal to bring it as close as possible to the genome of the extinct species. The next proposed stage is the creation of embryos with a "corrected" genome and their transplantation to a surrogate mother of a currently living species.

To date, scientists have obtained the genomes of about 20 extinct species, including the cave bear, the wandering pigeon, several representatives of the genus mammoths and moas, huge flightless birds that inhabited New Zealand and became extinct 3.5 thousand years ago. But no one has yet reported on the reconstruction of the genome of an extinct animal in its now living relative. Tom Gilbert, an evolutionary geneticist at the University of Copenhagen, started small. Together with colleagues from the Chinese University of Shantou, he focused on the Christmas Island rat that disappeared in 1908, which could be a dream candidate for the revival of an extinct species, given its close relationship with the gray rat, pasyuk, a well-studied laboratory rodent with a known complete genome.

Gilbert and his Chinese colleague Jianqing Lin isolated DNA from the skin of two Christmas Island rats preserved in formalin and repeatedly determined its sequence to obtain the most accurate genome. The old DNA was represented by small fragments, and therefore scientists used the genome of a gray rat as a reference, which allowed them to recreate as completely as possible the genome of an extinct rat.

Comparison of the two genomes showed that the genome of the rat from Christmas Island is missing almost 5%. The lost sequence contains information about almost 2,500 genes out of 34,000 suspected in the island rat. The recovered DNA has, for example, genes characteristic of this type of round ears, but important genes of the immune system and sense of smell are either absent or incomplete in it, the authors write in the journal Current Biology (Lin et al., Probing the genomic limits of de-extinction in the Christmas Island rat).

"This work demonstrates the difficulties, and perhaps even the ridiculousness of attempts to revive extinct species," said Victoria Herridge, an evolutionary biologist at the Natural History Museum in London.

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